Many different types of media mixing devices have been devised, including industrial, chemical and food and beverage mixers and preparation appliances. Blenders have a motor-driven blade mounted at the bottom of a pitcher to chop, stir, whip or blend solids or liquids loaded into the pitcher. Conventionally, the blender blade is mounted directly on a motor shaft, and is removable to allow the pitcher to be removed from a base in which the motor is housed. The motor is electrically driven at various selectable speeds. The necessity to remove the blade, or to mechanically disengage it from the driving shaft prior to removal of the pitcher is problematic.
Some attempts have been made to induce rotation of a mixing element or impeller by magnetic coupling with a mechanically driven magnet array. U.S. Pat. No. 3,554,497 describes a prior art stirring device which has a motor driven magnet in a housing, magnetically coupled to a stirring magnet inside of a vessel. The patent also describes magnetic field induced rotation of a stirring member in a vessel by electronically controlled driving of a fixed magnet array within a housing on which the vessel rests. Described for use in chemical laboratories and being explosion proof, the lack of any mechanical registry of the mixing element allows for irregular rotational motion and decoupling of the magnetic drive.
Some blending or stirring machines have also been provided with a heat source in contact with a vessel or pitcher in which a blade is mechanically rotated, in order to prepare foods or vegetables which are both stirred and heated. A heat source is in such devices located at the bottom of the vessel has the disadvantage of providing rather poor heat distribution through the liquid or food in the pitcher or vessel.